Bicycles intended for off-road and other rough terrain uses commonly have rear suspensions permitting sprung movement of the rear wheel relative to the bicycle frame. Suspensions of this kind have been developed to the level of multi-link systems, particularly four-bar linkages in which a rearwardly extending swing arm carrying the rear wheel is connected to a seat tube and/or down tube of the bicycle frame by way of pivot links. The swing arm, links and part of the tube or tubes form the elements of the linkage. The linkage geometry can be such as to not only provide effective wheel travel in response to the loads imposed by travel over uneven ground, but also to counteract a cyclic up-and-down motion or ‘bobbing’ effect of the rear suspension which otherwise arises as a reaction to and synchronous with the periodic power strokes transmitted to the pedal cranks of the bicycle. Examples of known four-bar linkage suspension systems include those disclosed in U.S. Pat. Nos. 5,678,837, 6,206,397, EP 1 026 073, GB 2 381 510 and FR 2774966.
Springing and shock absorption in such multi-link systems is commonly provided by a spring and damper unit. Units of this kind usually consist of a telescopic shock absorber located within and coaxial with a coil spring. Other forms of unit are equally possible including an integrated air spring and pneumatic shock absorber. The unit is normally coupled to the swing arm and the bicycle frame at respective pivot points selected to optimise the action of the unit, i.e. its influence on suspension travel. The end positions of the suspension travel are defined by settings of maximum compression and maximum extension of the unit. Such units function satisfactorily, but can, on occasions, be complicated to incorporate in a bicycle, sometimes to the extent of necessitating adaptation of the frame structure to accommodate the unit and its mountings. Weight and cost penalties result from the multiplicity of mountings for the unit and the various elements of the suspension linkage.
One approach to simplification of the mounting of a rear spring and damper unit in a bicycle is represented by the various constructions shown in DE 44 35 482, in which the embodiments of FIGS. 2 and 3 depict a spring and damper unit sharing the pivot points of pivot links which couple a rear wheel swing arm to a frame and which form, together with the frame and swing arm, a four-bar linkage. However, in the illustrated constructions the two links overlap in vertical direction entirely in the case of FIG. 3 and almost entirely in FIG. 2, with the consequence that the lateral rigidity of the linkage is compromised. Two nearly vertical lines of flexure run through, respectively, the forward pivot points of the links and the rearward pivot points of the links so that, with the additional load imposed by the shared coupling of the spring and damper unit, the rear suspension has only a limited capability of providing resistance to forces tending to deflect the rear wheel laterally relative to the frame. The solutions offered by DE 44 35 482 are therefore at the expense of the capability of the rear suspension to withstand critical deflections that can readily upset the tracking and poise of the bicycle.
It is therefore the principal object of the present invention to provide a bicycle with a rear suspension in which a spring and damper unit can be employed in association with a four-bar linkage with some mitigation of the above-mentioned weight and cost disadvantages, but without detracting from control of wheel travel and capability to accept the suspension loads encountered in normal use.
A subsidiary object is provision of a bicycle with sensitive components of a rear suspension located in a position having a degree of protection from mud and other contaminants thrown up by front and rear wheels of the bicycle.
Yet another subsidiary object is incorporation of an adjustment facility of simple design in a bicycle rear suspension to enable adjustment of the bicycle ride height.
Other objects and advantages of the invention will be apparent from the following description.